1. Field of the Invention
This apparatus lies in the field of filter apparatus. More particularly, it lies in the field of filter apparatus for separating particulate matter from a flowing fluid stream.
Still more particularly, this invention relates to a filtering apparatus for screening out sand from oil and gas flowing into a well, by permitting the oil and gas to flow through the permeable walls of the tubular elements and into the well tubing to the surface.
2. Description of the Prior Art
In the prior art there are a number of designs of sand screens for use in oil fields wherein a rigid skeleton structure is provided around which a wire is wound with suitable tension and suitable spacing, to permit the flow of oil without the flow of sand of sizes greater than a selected minimum. These designs typically require the use of a gravel pack sized to retain the formation sand which bridges and restrains the passage thereof into the production tubing.
Because of the large diameter and surface area of the prior art devices, the skeleton must be extremely rigid and strong to resist the forces acting radially inward on the wall by the sand, which compacts itself around the outside of the wire screen. Furthermore, in the prior art this single larger diameter screen has a maximum diameter which is the function of the diameter of the casing. There is no way of increasing the area except to make the device longer and longer, which entails considerable difficulty in providing suitable strength to the skeleton on which the wires are wound.